CODEWITHSUNDEEP
julia
CRquantum
CRquantum

Reputation: 626

How to prevent using global arrays in iteration in the module in Julia?

How to prevent using global array in iterations in the module?

module Mod
global AAA=Array{Float64,1}(undef, 999999999)
for  i in 1:100
      f(AAA, AAAupdate)   # function f take in AAA, update it and output the updated array as AAAupdate
      g(AAAupdate,AAA)  # function g take in the updatedAAA, and update it again to make a new AAA, and output the new AAA as AAA.        
end
end

As we can see, for each i loop,

the big array AAA first need to be input to function f, then updated to AAAupdate.

then function g takein the AAAupdate array, and further update it and form an updated array AAA.

Then in the next loop, the newly updated AAA will be read in function f again, and the process repeat 100 times.

Finally, after the 100 loops, AAA will be completely updated.

In this case, again since Julia discourages global stuff, are there ways to prevent making AAA a global array?

Upvotes: 1

Views: 67

Answers (2)

jling
jling

Reputation: 2301

it's fine to use global stuff if your entire module can only do one calculation at a time.

The traditional solution is to put that array into the same function where for loop is called:

function do_MC(L)
   AAA = Vector......
   AAA_up = similar(AAA)
   for i = 1:L
       f!(AAA, AAA_up)
       g!(AAA_up, AAA)
   end
   return AAA
end

But a global is fine speed-wise as long as you:

const AAA=Array{Float64,1}(undef, 999999999)

But here are two questions for you:

  1. Do you really need 999999999 elements? It's not like we're doing NOI competition where people just pre-allocate maximum length vector quick and dirty.
  2. Are you ready to make your module thread-unsafe because now user can't use that for loop in parallel.

Upvotes: 2

Nils Gudat
Nils Gudat

Reputation: 13800

I will cross-post my answer from Discourse, which essnetially implements the first paragraph of Jerry's answer:

julia> function main()
           AAA = zeros(5)
           for i ∈ 1:2
               f!(AAA)
               g!(AAA)
           end
           return AAA
       end
main (generic function with 1 method)

julia> main()
5-element Vector{Float64}:
 12.0
 12.0
 12.0
 12.0
 12.0

Upvotes: 2

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